1. Field of the Invention
The invention relates generally to a device structure and manufacture method of a transient voltage suppressor (TVS). More particularly, this invention relates to an improved device structure and manufacture method of TVS devices to handle dissipation of large amount of energy during a high transient surge and in the meantime maintaining a low capacitance for a transient voltage suppressor (TVS).
2. Description of the Relevant Art
The device configurations and method of manufacturing the transient voltage suppression (TVS) device are still confronted with the technical challenges that the TVS device fails due to overheating in handle a large amount of energy dissipation in the process of suppressing the transient voltage. Specifically, the transient voltage suppressors (TVS) are commonly applied for protecting integrated circuits from damages due to the inadvertent occurrence of an over voltage imposed onto the integrated circuit. An integrated circuit is designed to operate over a normal range of voltages. However, in situations such as electrostatic discharge (ESD), electrical fast transients and lightning, an unexpected and an uncontrollable high voltage may accidentally strike onto the circuit. The TVS devices are required to serve the protection functions to circumvent the damages that are likely to occur to the integrated circuits when such over voltage conditions occur. As increasing number of devices are implemented with the integrated circuits that are vulnerable to over voltage damages, demands for TVS protection are also increased. Exemplary applications of TVS can be found in the USB power and data line protection, Digital video interface, high speed Ethernet, Notebook computers, monitors and flat panel displays.
The challenges for the TVS device to absorb large amount of energy in short period of time is increased due to the requirements of the TVS performance with common IEC 61000 Standards of 8×20 μSecs, 10×1000 μSecs pulse surge current. With large amount of energy dissipation, the most common TVS failures often occur when the metal melts down due to overheating. It is well known that the silicon as part of the TVS device can sustain significant higher power dissipation than the metal. While the metal layer often formed near the top surface of the TVS structure and commonly implemented as electrodes or electrical contacts, the metal layer tends to melt down due to overheating. The over voltage protection functions of the TVS device are therefore compromised due to these melt down failures.
FIG. 1 is a cross sectional view of a conventional TVS device. The device structure has an intrinsic limitation due to a shallow blocking junction caused by a topside N diffusion manufacturing process. As a result, the voltage blocking region is closer to the surface that is near to the metal layer commonly formed on the top surface as electrical contacts. As the semiconductor device experiences a high transient voltage surge, the blocking junction absorbs a large amount of energy thus causing the temperature to rise rapidly. The elevated temperature takes place locally near the metal may lead to overheating followed by melting the metal disposed near the blocking junction area thus causes the TVS to fail.
Therefore, a need still exists to provide new manufacture methods for the TVS devices with improved processes to produce new device structures such that the above discussed problems and limitations can be resolved.